Honeywell VRX180 user manual Function Block Configuration of a Typical Ratio Control Loop

Programming Function Blocks and Features

AO2 BC

UNITS = FPS

INPUT TYPE = LINEAR

DIRECT/INDIRECT/SQRT = SQRT

RANGE LOW = 0

RANGE HIGH = 40

CIRCUIT LOW = 1

CIRCUIT HIGH = 5

		ELECTRICAL UNITS = VOLTS				FEEDBACK
AIR	∆	P	AI2	AI2 OV				4 TO 20 mA
					PV
SIGNAL								TO AIR FLOW
								CONTROL
						LP2	LP2 OV	VALVE
								IN AO2

∆			AI3 OV	WILD		⋅	+
				VARIABLE
FUEL	P	AI3
SIGNAL
UNITS = FPS						RATIO	RATIO
					SETPOINT		BIAS
INPUT TYPE = LINEAR
DIRECT/INDIRECT/SQRT = SQRT				TYPE = RATIO
RANGE LOW = 0				SETPOINT #1 = 500
RANGE HIGH = 40
CIRCUIT LOW = 1				WILD VARIABLE = AI3 OV
CIRCUIT HIGH = 5				RATIO SETPOINT = 0.50
ELECTRICAL UNITS = VOLTS				RATIO BIAS = 0.75

GAIN = 10

RESET = 1

RATE = 0

SP2	OUTPUT TYPE = CAT
	IN LOW LIMIT = 0
	IN HIGH LIMIT = 100
	OUT LOW LIMIT = 4
	OUT HIGH LIMIT = 20

Working set point of loop when use of WILD VARIABLE is desired to establish proper control of PV. If ratio control using WILD VARIABLE must be temporarily suspended, loop’s working

set point may be switched ON LINE to SETPOINT #1 via “SP (Set Point Select)” key on instrument’s front door.

Figure 4-1 Function Block Configuration of a Typical Ratio Control Loop

When the ratio control loop in Figure 4-1 is brought ON LINE, its ON LINE display must be accessed to allow the instrument’s SP (Set Point Select) key to be operational. To make the working set point of the ratio control loop equal the equation (WILD VARIABLE X RATIO SETPOINT) + RATIO BIAS, then select the TUNE LOOP menu item TOGGLE SETPOINT SOURCE so that an “SP2” is seen in the loop’s ON LINE display. Note that within the ratio control loop’s programming menu (accessed under PROGRAM CONTROL LOOPS), you will not find a SETPOINT #2 menu choice. The ratio control loop function block operates with the formula (WILD VARIABLE X RATIO SETPOINT ) + RATIO BIAS assuming all the functionality of the ratio loop’s second set point. Pressing the SP key to switch the working set point of a live ratio control loop from SP2 to SP1 will essentially suspend any ratio control and cause the loop to behave like a standard PID controller. This standard PID loop will have a local set point equal to the value programmed for SETPOINT #1. To control the process variable using a fixed set point that is independent of the loop’s WILD VARIABLE input, toggle the ratio control loop’s working set point to SP1.

100 Video Recorder – User Manual